UNESCO recognised the Wadden Sea National Park on the west coast of Schleswig-Holstein as a biosphere reserve back in 1990. The five inhabited Halligen islands were added as a development zone in 2005.
The ebb and flow of the tides define the Wadden Sea and the small marsh islands (which can't be found anywhere else in the world), with large mudflat areas being flooded twice a day and the water often then disappearing again. Visitors can explore this fascinating habitat on guided tours of the mudflats, giving them the chance to wander about on the seabed and spot lugworms, cockles and crabs. Ships are also on hand to transport people to visit the seal colonies. It's business as usual on the traditional Halligen islands of Gröde, Hooge, Langeness, Nordstrandischmoor and Oland. The flooding process is totally normal for the residents of the Halligen islands (of whom there are just under 300), who live in houses on man-made mounds of earth shaped like hills to be safe.